1. Field of the Invention
The invention relates to a method and a device for forming an extinction blocking signal for gate-turn-off power semiconductors in static converters, for suppressing unacceptable extinction attempts.
For example, an application of the invention is possible in the case of GTO pulse-controlled inverters for traction drives.
2. Description of the Related Art
Such a method is known from German Published, Non-Prosecuted Application DE-OS 37 27 996. The method described therein for suppressing unacceptable extinction attempts in gate-turn-off power semiconductors in static converters, is characterized by the fact that a measurement quantity composed of the actual anode current or load current of the semiconductor and the product of the derivation of the actual anode current with respect to time and the maximum turn-off delay time is formed and compared with an adjustable maximally switchable anode current. In that method extinction commands that occur are suppressed when the measurement quantity being formed reaches or exceeds the maximally switchable anode current.
GTO thyristors are gate-turn-off power semiconductors for very high powers. They can turn off currents below a limit value ITQ (which is a periodically interruptible anode current of a GTO thyristor) but can conduct very much higher currents without difficulties if no turn-off attempt is made. It is therefore logical to block the turning-off of GTO thyristors when the GTO current exceeds the limit value ITQ.
A GTO thyristor interrupts the current only at certain time after the turn-off command, which is the so-called storage time. During the storage time, the anode current of the GTO thyristor can continue to rise. The method of the predictive, extinction block according to German Published, Non-Prosecuted Application DE-OS 37 27 996 therefore predicts the current to be expected at the instant when the GTO thyristor is turned off, from the actual GTO current and its actual current rise (di/dt) during the storage time, and compares it with ITQ.
Instead of the GTO current, the load current of the static converter can be used in the known method since that is measured in any case for control purposes and in most cases it only differs little from the GTO current. In contrast, the di/dt values of the GTO currents are measured individually for each GTO thyristor by means of sensing coils (current rise sensing devices).
In order to avoid interfering parasitic inductances, the di/dt sensing coils can only be installed in such a manner as to exposed them to the currents of the protection networks of the GTO thyristors. The protection networks are LC structures (wherein L is inductance and C is capacitance) which oscillate with more or less intensity depending on the circuit of the power section being used. Since the di/dt sensing coils also measure the snubber currents in the known method, errors in the formation of the extinction blocking signal can occur in practice because of the high di/dt values of the snubber oscillations.
If the di/dt value of the snubber current acts in the same direction as that of the GTO current, the extinction block is wrongly and unnecessarily triggered. Such mistriggerings must be subsequently filtered again at the level of signal processing. If the di/dt value of the snubber current opposes that of the GTO current, the extinction block is based on too small a di/dt value and may therefore not trigger even though that would be required. The consequence is a risk of destruction of the GTO thyristor concerned.
It is accordingly an object of the invention to provide a method and a device for forming an extinction blocking signal for gate-turn-off power semiconductors, which overcome the hereinafore-mentioned disadvantages of the heretofore-known methods and devices of this general type and which operate in a simple manner to ensure a maximum utilization without risk of destruction for the power semiconductors and largely avoid functional disturbances due to snubber currents in protection networks for the power semiconductors.